1. Field of the Invention
The present invention relates to a super-resolution processor and a medical diagnostic imaging apparatus for performing super-resolution processing on volume data or multislice data collected by an X-ray CT scanner.
2. Description of the Related Art
X-ray CT scanners have made considerable progress and, in response to strong demand for higher-definition (higher-resolution) imaging from a medical field, multislice X-ray CT scanners have recently been developed and become widely available. The multislice X-ray CT scanner includes an X-ray source for emitting fan-beam X-rays having a broadening width in a slicing direction (along the base) and a two-dimensional detector with a structure in which multiple rows (four, eight, sixteen, etc.) of detecting elements are arrayed in the slicing direction, which are operated by multiscanning or helical scanning. This provides high-accuracy volume data across the wide range of a sample in a short time as compared with a single-slice X-ray CT scanner.
The volume data obtained in such a way is recently not only displayed for observation but also used in various applications. For example, for medical use, it is used for measuring the ratio of angiostenosis, aneurysm, or varicose veins. Specifically, an X-ray contrast medium is given to a sample for imaging by an X-ray CT scanner, so that volume data can be provided in which the distribution of the contrast medium flowing in the blood vessel is imaged. Accordingly, the ratio of angiostenosis and the size of aneurysm or varicose veins can be measured from the distribution of the CT value of the contrast medium imaged in the volume data. For example, the ratio of angiostenosis is obtained by measuring the thickness of the inner wall of the blood vessel (the range occupied by the contrast medium) from the volume data and comparing the thickness of an apparently normal region of the blood vessel to that of a thin region. For the measurement of the thickness of a blood vessel, a threshold for a CT value is generally set.
JP-A-11-342132 discloses another example of the process of volume data acquired from not only the X-ray CT scanner but various medical imaging scanners including an ultrasonic diagnostic imaging scanner and a magnetic resonance imaging scanner. The scanners described in JP-A-11-342132 are intended for accurate blood-vessel measurement based on display images, wherein a region of interest is set that crosses the wall of a blood vessel vertically on the tomogram of the vessel and the size of the vessel is measured from the profile of the pixel values in that region. JP-A-2000-350726 describes another example intended for accurate measurement of the length of a region of interest (a blood vessel, bowels, etc.) having curvature in a direction that is not in parallel to the projection plane using a maximum intensity projection (MIP) image.
Not only the X-ray CT scanner but also all imaging scanners have resolution limit that depends on the pitch of the detecting elements of their detectors. Referring to FIG. 11, particularly, the CT image of the X-ray CT scanner is formed as a reverse projection sum of a large number of views. Accordingly, blurring that depends on the resolution limit appears on the image as a result of multidirectional multiple combination of data profiles of one view at a minute point. In other words, the CT image can be stated as the intensity distribution function of a minute point image which represents blurring, that is, the assembly of point spread functions (PSFs).
However, no consideration is given to the blurring under present circumstances.